They just cut and bin the books after they've been scanned, the bins are taken to the local disposal, most municipalities have a garbage dump, some burn the trash.

An ai trained on unique data is more valuable if you don't share the data it was trained on to your competition, your LLM gains an edge.

If I found a unique handwritten book from the 18th century, than I proceed to read it and memorise then burn it, I'll be the only one to posses the knowledge of it.